Make compatible with Docker Metadata action

It would be really nice if this action were compatible with the [Docker Metadata action](https://github.com/docker/metadata-action), so that tags could be generated by that action and easily passed to this action.

Right now, if you do this:

```yml
- id: metadata
uses: docker/metadata-action@v4
with:
tags: |
type=ref,event=branch
type=ref,event=pr
type=semver,pattern={{version}}
- uses: devcontainers/ci@v0.3
with:
imageTag: "${{ join(steps.metadata.outputs.tags) }}"
```

The result is a Docker error, because `steps.metadata.outputs.tags` is already in the format `"{image}:{tag}"[]`, and this action prepends each tag with `{image}:` again. Docker doesn't like `-t {image}:{image}:{tag}` and errors out.

If this action could check each tag to see if it's already prepended with the image name before doing so, then I think it would be directly compatible with the official Docker action.